Various materials which are contained in exhaust gas which is exhausted from an engine of an automobile or the like, particularly a diesel engine are cause of air pollution, and have generated various environmental problems until now. Particularly, it is said that particulate matter (PM) which is contained in the exhaust gas is a cause of generation of allergic symptoms such as asthma or hay fever.
In general, in a diesel engine for an automobile, as an exhaust gas purifying filter for collecting particulate matter, a DPF (Diesel Particulate Filter) which has a sealing type ceramic honeycomb structure (filter substrate) is used. In the honeycomb structure, both ends of a cell (gas passage) of the ceramic honeycomb structure are sealed in a checker pattern, and particulate matter is collected when the exhaust gas passes through micropores in partitions between cells (for example, refer to PTLs 1 and 2)